The reason that older cities such as Washington and Ottawa are successes whereas some newer cities such as Naypidaw and Brasilia are considered failures is due

The reason that older cities such as Washington and Ottawa are successes whereas some newer cities such as Naypidaw and Brasilia are considered failures is due to designers of the time trying to fix urban issues with modern solutions but fundamentally not understanding at all what makes cities liveable. The designers had no concept that their 'fix' would have side effects that would make things worse. A major issue is that many of these newer cities are designed not at the human scale, but at car scale. The result is massive roads and lengthly blocks that are unwalkable for pedestrians. This results in no street life and a desolate experience. The designers believed that by building wide roads great for moving cars they were fixing traffic problems that traditional cities have, but the unintentional side effect is that the experience for people on the ground is terrible.